1 ======================================================

2 PART 1 STARTS HERE

3 ======================================================

4 From: wagons@connriver.net (Daniel Wing)

5 Subject: Long Technical Post 1

6 Date: 1998/05/25

7 Message-ID: <wagons-0301041020310001@port-1-26.wellsriver.connriver.net>

8 Organization: Cookeville Garage

9 Newsgroups: rec.food.sourdough

10

11

12 Some members of this newsgroup will remember that I have posted some of

13 the content of my correspondence with Michael Ganzle, a German sourdough

14 researcher. He has recently reviewed a proof of a book I have written

15 about masonry ovens and naturally fermented bread, and has commented in

16 detail. Those comments will interest those of you who are interested in

17 the science and technology of sourdoughs. This post and others that follow

18 are for you. If you ARE NOT linterested in the subject, stop here, and

19 save yourself from confusion and frustration.

20 In each section Michael quotes a sentance from the book, and then responds:

21 ------------------------------------

22 "witness the profusion of instant yeast brands-- while the opposite is true³

23 **

24 I strongly appreciate the notion that the "time equals money equation³ is

25 not true for sourdough bread or any kind of other fermented foods-- wine,

26 soy sauce, cheese, vinegar, fermented sausage: they usually get better if

27 they are fermented for a long time (the definition of "long³ varies,

28 though, with the different foods).

29 -------------------------------------

30 "I triple it by mixing it with its weight of water and its weight of flour³

31 **

32 There is a microbiological explanation for the three stage sourdough

33 processes. Microbial growth can be divided in three stages. When the

34 organisms are transferred to a new environment (e.g. by refreshing a

35 sourdough that has been in the refrigerator), they take some time to

36 adapt; no growth occurs ("lag phase³). Once the organisms are familiar

37 with the new environment, they start to grow exponentially, meaning one

38 doubling of cell counts in a given time (generation time), so called "log

39 phase³. Eventually, the culture will become stationary, i.e. the organism

40 have run out of food, or are inhibited by the metabolic end products. For

41 effective sourdough fermentation, one needs a lot of metabolically active

42 cells. After three or more refreshments, the organisms will reliably start

43 to grow soon after inoculation and will produce enough carbon dioxide.

44 Things are different with yeast dough, though: there simply are so many

45 cells that these have to cough only once to raise the dough.

46 --------------------------------------------

47 "the time it was inoculated and to the temperature at which it is kept

48 than with the size of the inoculation.] Let's call this the second leaven³

49 **

50 Comment No1: Weıve been doing quite some work to figure out which factors

51 affect microbial growth in sourdough. Iıve done some work in vitro (which

52 is about to be published: Gänzle et al., Modeling of growth of

53 Lactobacillus sanfranciscensis and Candida milleri in response to process

54 parameters of the sourdough fermentation, Applied and Environmental

55 Microbiology, July 1998); and a colleague of mine, Markus Brandt, has

56 tried to figure out how my "model predictions³ work out during the actual

57 dough fermentation. Taken together, one can state the following:

58 A) The optimum temperature for sourdough lactobacilli is 32 - 33°C. At

59 37°C and 20°C, the generation time is twice as long.

60 B) At 39 and 15°C, the generation time is four times as long.

61 C) At 41°C and 4°C, no growth is observed.

62 For the yeasts, the figures are as follows:

63 A) 28°C(optimum growth)

64 B) 32/20 (double generation time)

65 C) 34/14 (fourfold generation time)

66 D) 35°C, 8°C: no growth.

67 So: if several refreshments are done above 32°C, the yeasts will drop out

68 eventually. The optimum pH for lactobacilli is 5.0 - 5.5 (which is the

69 initial pH of a sourdough with 5 - 20% inoculum), the minimum pH for

70 growth is 3.8 (they usually produce acid until pH 3.6 is reached).

71 Lactic or acetic concentrations donıt affect growth of lactobacilli very

72 much: this is the reason why the buffering capacity of the flour is so

73 important for the organism (a high buffering capacity in high ash flours

74 means that the lactobacilli produce much acid until the critical pH is

75 reached). It also means, that in doughs that are continuously operated

76 with a high inoculum (more than about 30%), youıll find more yeasts and

77 fewer lactobacilli. Eventually, the lactobacilli flora may change, with

78 more acid tolerant lactobacilli (e.g. L. pontis) prevailing. Such a

79 sourdough is found in the Vollmar and Meuser continuous sourdough

80 fermentation machines (there are 6 operating in Germany, and a diploma

81 candidate in our department characterised the microflora of several of

82 these: as the machine is operated with a 50% inoculum, the pH is never

83 above 4.1 - 4.3, and no L. sanfranciscensis is found in those doughs).

84 Yeasts are different: they donıt mind the pH at all, but are strongly

85 inhibited by acetic acid, and to a much lesser extend by lactic acid.

86 Increasing salt concentrations inhibit growth of lactobacilli, but yeasts

87 tolerate more salt. No salt is added to the sourdough until the final

88 bread dough, but the dough yield affects the salt concentration: with a

89 low dough yield (little water), the salt (ash) is dissolved in a smaller

90 water volume, and the salt concentration goes up: resulting in a slower

91 fermentation.

92 So much for the "in vitro³ theory. Surprisingly, Markus has found most of

93 the predictions to come true when he was looking at the cell counts at

94 different temperature, size of inoculum, salt concentration, and pH in rye

95 dough. The variation of the inoculum size was interesting: If he reduced

96 the inoculum size by 2, he had to wait almost exactly one generation time

97 (one doubling time of the lactobacilli) longer until the dough has reached

98 the same cell counts, pH, titrable acidity, and so on as the dough with

99 the higher inoculum. This was true for inoculum sizes between 1% and 20%:

100 at 50% inoculum, the pH is so low that the lactobacilli donıt really grow

101 well, and at an inoculum size of 0.1%, the pH and/or the oxygen pressure

102 in the dough are so high that the cells have a lag-time (see above) of an

103 hour. Thus, a scanty inoculum means one generation time longer

104 fermentation.

105 The generation time of L. sanfranciscensis in rye dough at 28°C is a

106 little less than an hour (figures may vary with different strains in

107 different flours, but itıs not much more or less than that), so if the

108 inoculation size is reduced from 20 to 2.5%, itıll take about three hours

109 more until the dough is ripe.

110 The question is, whether these findings are true for all flours and for

111 all organisms. The strain isolated by Kline and Sugihara does not differ

112 very much from the two strains Iıve been looking at. All the literature

113 available tells me that - as long as weıre looking at sourdoughs with a

114 tradition of continuous propagation - the system behaves the same way.

115 Differences may be between rye flour and white wheat flour: in white wheat

116 flour, the enzyme activities are so low that the organisms may run out of

117 food before the critical pH (lactobacilli) or the critical acetic acid

118 concentration (yeasts) is reached.

119 =============================================================

120 This discussion continues in the next post-- DCW

121 --

122 Dan Wing

123 Wagons@connriver.net

124 ======================================================

125 PART 2 STARTS HERE

126 ======================================================

127 From: wagons@connriver.net (Daniel Wing)

128 Subject: Long Technical Post 2

129 Date: 1998/05/25

130 Message-ID: <wagons-0301041021200001@port-1-26.wellsriver.connriver.net>

131 Organization: Cookeville Garage

132 Newsgroups: rec.food.sourdough

133

134

135 Rye is second to wheat as a bread grain

136 **

137 Comment No2: If discussing rye, it may be of importance, that rye quality

138 depends heavily on the weather conditions during the harvest: if is is

139 very humid before and during the harvest, sprouting starts, leading to

140 increased amylase activity. In a dry year, the amylase activities may be

141 rather low, so that the problem with the acidification is not very

142 prominent. It may also be noted that rye not only has a higher amylase

143 activity,a but also a higher protease activity, which is important for the

144 flavor development.

145 ---------------------------------------------------------

146 In all, about 72 percent of the original kernel is left in most of the

147 white flour produced in the United States.

148 **

149 In Germany, the most common bread flour is wheat type 1050 (1.050 g ash

150 per kg) or rye type 1180. Many breads are "Vollkornbrot³. Type 550 (or 55)

151 is used only for white wheat bread, not a very big share in the market.

152 -----------------------------------------------------

153 Rye flour is commercially ground to a range of colors and particle sizes,

154 and the nomenclature is confusing.

155 **

156 If very coarsely groung flour is used, it should be swollen in water

157 before the dough mixing, Otherwise, it will take up water during dough

158 fermentation and proofing, and result in too stiff doughs. This is called

159 "Quellstueck³ by German bakers. As far as the enzyme activities go, see

160 comment No2 above. The difference in enzyme activities is also important

161 for the microorganisms: in rye flour they always have enough sugar

162 available due to the high enzyme activities, whereas in white wheat

163 flours, glucose (but not maltose) may be depleted during the fermentation.

164 ----------------------------------------------------------------

165 Rye flour contains a great deal of amylase. Rye amylase resists

166 inactivation by heat to a greater extent than wheat amylase. It is so

167 resistant to inactivation that it is still active when the gelatinization

168 temperature of rye starch is reached in the oven

169 **

170 This is a very nice explanation. Also: see above (Comment No2)

171 ----------------------------------------------------------

172 No laboratory test assesses taste, even though there are real differences

173 in the taste and texture of bread baked from otherwise similar flours.

174 **

175 This would be impossible, since the flour has no flavor whatsoever. Iıve

176 been preparing a research proposal recently with Markus Brandt and Prof.

177 Hammes in our lab, and Prof. Schieberle, probably the best expert in

178 flavor chemistry of bread, so Iıll go into some detail (and refer to it as

179 comment No3 later on). It may be useful to distinguish between taste and

180 aroma. Taste happens on the tongue, where only salty, bitter, sweet and

181 sour can be evaluated. Aroma is percieved in the nose: during chewing, the

182 volatile compounds diffuse to the receptors (mind that acetic acid, but

183 not lactic acid is volatile. Thus, the latter is just sour, while acetic

184 acid has aroma). There are about 15 compounds each (about 10 of them are

185 the same for wheat and rye bread, furthermore, crust and crumb have

186 different aroma volatiles) with which the impression of rye or wheat bread

187 is given (This is work of Prof. Schieberle in Munich).

188 To group the compounds according to their generation in dough, one may say

189 that:

190 i), they are produced by fatty acid oxidation by cereal enzymes upon dough

191 mixing (several baking aids contain soy flour with additional lipoxygenase

192 activity, and prolonged storage of whole flour leads to rancidity as

193 well). These compounds have a "green³, "bitter³ "tallowy³ or "metallic³

194 taste - not very pleasant. Lactic acid bacteria and yeasts do inactivate

195 these compounds in part, thus, fermentation reduced the "rancidity³ of the

196 bread.

197 ii) aroma compounds are produced by yeasts and lactobacilli. More of them

198 by yeasts, probably, though acetic acid also plays an important role.

199 These compounds often give a "flowery³, "yeasty³ or "malty³ flavor.

200 iii) The Maillard reaction is extremely important, especially for the

201 crust aroma compounds. However, the precursor chemicals for this type of

202 reactions are amino acids, and the levels of amino acids in flour is verym

203 low. In wheat, there is little, if any proteolytic activity (proteases

204 degrade protein to amino acids), so, whatever amino acids there are

205 produced by enzymes of lactic acid bacteria (there has been nice work done

206 on proteolysis in wheat dough by Dr. Marco Gobbetti at the University of

207 Perugia). In rye, the proteolytic activity of the flour is much higher,

208 but the proteases need acidification to a pH below 5 to have their optimum

209 activity (and, of course, a long fermentation time gives the enzymes more

210 time to work). Sourdough yeasts are consuming amino acids, meaning a

211 sourdough with a high yeast count has fewer amino acids than a dough

212 containing only lactobacilli. Addition of excess amounts of bakerıs yeast

213 (>4%) also leads to an increase of Maillard compounds, but that may not be

214 the aroma a sourdough baker is looking for. The most important flavor

215 compound in rye crust, methional, as well as in wheat crust,

216 2-acetyl-pyrroline, are Maillard products of the amino acids methionine

217 and ornithine, respectively.

218 As I mentionned, weıve been preparing a research proposal to figure out

219 which of the aroma compounds or aroma precursors (meaning chemicals

220 converted to aroma compounds during baking) are formed by which

221 microorganisms. In other words, other than acetic acid production, we

222 donıt know whether or not aroma is produced by yeasts and lactobacilli of

223 sourdough. There are a few good working hypotheses: Some, but not all

224 strains of L. sanfranciscensis convert arginine to ornithine (MOST

225 important flavor precursos in wheat), so this metabolic activity may be of

226 importance. Several other compounds are produced by yeasts (but we donıt

227 know whether the sourdough yeasts are more active than bakerıs yeast), and

228 all L. sanfranciscensis does convert the fatty acid oxidation products to

229 chemicals with less or no aroma intensity - but how this activity compares

230 to straight, bakerıs yeast dough, we donıt know.

231 ============================================

232 continued in next post-- DCW

233 --

234 Dan Wing

235 Wagons@connriver.net

236

237 ======================================================

238 PART 3 STARTS HERE

239 ======================================================

240

241

242 From: wagons@connriver.net (Daniel Wing)

243 Subject: Long lTechnical post 3

244 Date: 1998/05/25

245 Message-ID: <wagons-0301041021590001@port-1-26.wellsriver.connriver.net>

246 Organization: Cookeville Garage

247 Newsgroups: rec.food.sourdough

248

249

250

251 Amylase digestion of this damaged starch provides sugar for fermentation

252 and produces dextrins, a class of polysaccharide that is quite

253 hygroscopic.

254 **

255 See comment No2: lactobacilli and yeast rely on the amylase of the grain

256 as they donıt have starch degrading enzymes. A Spanish group has looked

257 for the development of maltodextrins during sourdough fermentation: as

258 lactobacilli and yeasts donıt like the oligosaccharides, they accumulate

259 during fermentation. The Spanish (C. Collar and M. Martinez-Anaya in

260 Valencia, Spain) think that maltodextrins may delay bread staling, though.

261 ----------------------------------------------------

262 because that enzyme (PHYTASE) is most active in dough between pH 4.3 and

263 4.6, prolonged fermentation with mixed cultures (an acid medium) will

264 **

265 It is true that the enzyme is most active IN DOUGH between pH 4.3 and 5,

266 however, the reason is not optimum enzyme activity at this pH, but the

267 fact that CaMg-Phytate is insoluble and thus not available for enzymatic

268 cleavage at a higher pH. (The first work during my diploma thesis was to

269 look for phytase enzymes in lactobacilli from sourdough. After 8 weeks, I

270 figured out that there is none, and shortly thereafter it became clear

271 that both wheat and rye have sufficient phytase activity, all it takes is

272 some acidification).

273 -----------------------------------------------------

274 I chose to write "natural leaven" because it is less awkward than "mixed

275 ferment cultured from the environment and sustained with repeated

276 inoculation."

277 **

278 "Sustained with repeated inoculation³ is better than anything I was

279 writing to say the same thing. Cultured from the environment³ is certainly

280 true - L. sanfranciscensis and the yeasts must come from somewhere - but

281 somewhat misleading, as these organisms most probably do not originate

282 from the grain, or the flour (Marco Gobbetti, whom I mentionned earlier

283 has been looking for L. sanfranciscensis on all kinds of Italian wheat

284 flours, and he has not found any. In every Italian dough "sustained with

285 repeated inoculation³ youıll find L. sanfranciscensis to be the dominating

286 species, though. No other scientist has been able to isolate L.

287 sanfranciscensis from any other source than sourdough, but all sourdough

288 "sustained etc.³ Contain this organism as the dominating flora. A possible

289 source may be the humans: there are all kinds of lactobacilli thriving in

290 the mouth, the intestines, etc. Hammes met a South African Microbiologist

291 who claimed to have isolated L. sanfranciscensis from the teeth of

292 pre-school children. The data is not published, so I donıt know what

293 science is behind this claim. But, whereever L. sanfranciscensis comes

294 from, it most probably does not come from the flour. (Thats comment No4)

295 --------------------------------------------------------

296 Natural leavens are not all the same. Not only are there many strains of

297 yeast and bacteria that can form them, we need terms in English for the

298 various stages of natural leavens.

299 **

300 One may think of all the "sourdough stages³ as just a piece in a infinite

301 chain of repeated inoculations. Some sourdoughs are quite close to

302 infinity, as far as the generations go. You certainly know Carl Griffith

303 sourdough (claimed to have survived since the days of the Oregon Trail);

304 the dough weıve been working with, Böcker Reinzucht Sauer, a rye starter

305 that thas the reputation of being one of the best rye starters available

306 (Spicher says so, we do, and the Spanish group has been working with it as

307 well), is well above 50 yeast "old³. Then, the definition of e.g. "three

308 stage sourdough processes³ does make no sense. What makes is fascinating

309 is that the microbiology of Böcker Reinzuch Sauer HAS NOT CHANGED in the

310 past 30 yeast, i.e. since people started to do microbiology with the

311 dough. There are two strains of L. sanfranciscensis, and one yeast, C.

312 milleri. The "modeling³ I mentioned in comment No1 was done with these

313 three organisms. Remarkably, the two strains of L. sanfranciscensis

314 reacted almost identically on changes of pH, temperature, etc. Then, the

315 definition of e.g. "three stage sourdough processes³ does make no sense.

316 -----------------------------------------------------

317 This selection leaves it (COMMERCIAL YEAST) specialized for a narrow range

318 of fermentation characteristics that favor rapid gas production over

319 flavor production or other possibly desirable qualities (resistance to

320 bread spoilage, for instance).

321 **

322 This could be also said for sourdough lactobacilli and yeasts: As the

323 dough is continuously refreshed, those strains are selected that grow

324 fastest in dough. This is probably a much more harsh and effective

325 selection than what is done for the bakerıs yeast. Fortunately, what is

326 good for the sourdough lactobacilli seems also to be good for bread

327 quality (There are other microorganis in fermented food that require the

328 man-made habitat: e.g. Tetratenococcus halophilus growing only in soy

329 mashes, and Oenococcus oeni, occuring in wine only.) What is important, is

330 that as soon as you change your parameters, you may change the microflora.

331 E.g., if the dough is fermented at 33 instead of 28°C, yeasts will drop

332 out, and above 37 - 38°C, the flora will change altogether, with

333 thermophilic lactobacilli dominating. See comment No1.

334 ---------------------------------------------------------

335 The yeast and bacteria in natural leavens are considered native or wild

336 because the cultures are started with organisms recovered from

337 environmental surfaces,

338 **

339 The fermentation starts with flour microorganisms, but - see comment No4 -

340 the sourdough lactobacilli and yeasts do probably not originate from the

341 grain. And later: the organisms have been refined by thousands and

342 thousands of sourdough - refreshments, much more effective than any

343 microbiologist of food scientist could ever be. (Besides, we know what

344 kind of organisms do grow in sourdough - but how flavor production takes

345 place, and which fermentation products delay bread staling is largely

346 unknownm - so other than gas production, I could not think of a property

347 of lactobacilli in which to select a strain. And gas production, as youıve

348 rightfully pointed out, is certainly not the right criterium.)

349 ----------------------------------------------------------

350 The conditions under which a culture is developed and then maintained can

351 select out strains of yeast and bacteria that have special

352 characteristics, and the typical yeasts present in the air and soil in

353 different locations also vary somewhat in their properties and their

354 interactions with lactobacilli. This kind of co-evolution makes some

355 natural leavens remarkably stable when regularly maintained. The more

356 regular and consistent the maintenance, the more predictable the rising

357 power, microbiological composition, acid balance (acetic/lactic) and acid

358 production will be.

359 **

360 This is important (although I donıt think that the yeasts from air and

361 soil do matter). But the consistency in maintenance is crucial (one is

362 allowed to err to one side or the other from time to time, though).

363 -------------------------------------------------------------------

364 ============================================

365 continued in next post-- DCW

366 --

367 Dan Wing

368 Wagons@connriver.net

369

370

371 ======================================================

372 PART 4 STARTS HERE

373 ======================================================

374 From: wagons@connriver.net (Daniel Wing)

375 Subject: Long Technical Post 4

376 Date: 1998/05/25

377 Message-ID: <wagons-0301041022540001@port-1-26.wellsriver.connriver.net>

378 Organization: Cookeville Garage

379 Newsgroups: rec.food.sourdough

380

381

382

383 Since many people new to natural leavens would like to bake San Francisco

384 sourdough, Desem bread, or German rye bread, let's look at some of their

385 characteristics, as determined by their leavens, ingredients, and

386 processes.

387 **

388 The microflora of German rye sour and Sanfrancisco sourdough is (almost)

389 identical. The difference is raw material and production process. Prof.

390 Hammes thinks that L. sanfranciscensis isolated from wheat or rye may have

391 different properties (e.g. degradation of arginine to ornithine, see

392 comment No3, or proteolytic activity (see comment No2: wheat has less

393 proteolytic activity by itself than rye). He still has to prove his point,

394 though.

395 -----------------------------------------------------------

396 That yeast is also resistant to a natural antibiotic made by the bacteria.

397 **

398 The most "antibiotic³ compound in sourdough is acetic acid. Although I

399 mentionned earlier that Candida milleri from Böcker Reinzucht Sauer (The

400 Saccharomyces exiguus described by Kline and Sugihara has been renamed to

401 Candida milleri as well) is more sensitive to acetic acid than the

402 lactobacilli, it certainly is much more resistant than bakerıs yeast.

403 Gobbetti says that L. sanfrancisco produces other organic acids that may

404 inhibit yeast growth, but I donıt know wheter or not the concentration in

405 the dough is high enough to make a difference. As far as I know, no other

406 antimicrobial compound in dough has been characterised.

407 -----------------------------------------------------------

408 Most German rye bread has at least 30 percent rye

409 **

410 I have the figures: 60% is "mixed rye bread³ containing both rye and

411 wheat, but more of the former. As far as the bread goes, rye only about as

412 important as wheat only. The situation is different for bagels, pretzels,

413 and so on. There is increasing interest in wheat sourdoughs: the 1 - 5%

414 addition of sourdough, which is sometimes replaced by a dried and "dead³

415 sourdough works, but not quite as well as it could. Which is why industry

416 is funding flavor research at the Universities of Hohenheim and Munich...

417 ----------------------------------------------------------

418 Vollmar and Meuser showed that the rate of bacterial reproduction after

419 inoculation is self-regulated, within limits: if you add a small inoculum,

420 the bacteria will multiply faster than they will if it is larger, so the

421 static population (say 1,650 million cells/cc) is reached at the same time

422 in either case, about three and one-half hours.

423 **

424 The Vollmar and Meuser sourdough machine is not a very good example: as

425 pointed out in comment No1, it operates with an inoculum of 50%, which

426 makes the dough so acid from the beginning on the the lactobacilli donıt

427 like to grow fast. Between 1 and 20% inoculum, lactobacilli grow at the

428 same speed (giving rise to the dependency of fermentation time and

429 inoculum size explained earlier). The Vollmar and Meuser machine also has

430 a rather high yeast content (if youıve read their publication in Cereal

431 Chemistry; yeasts are above 100 million or more than 10% or the total cell

432 counts, while "normal³ starters such as the Sanfrancisco starter of the

433 Böcker Reinzucht Stater have only around 10 million or about 1% of the

434 total cell count.

435 --------------------------------------------------------

436 When cultures are fermented at higher temperatures, non-pathogenic

437 acid-tolerant contaminants such as Pediococcus (makes too much lactic

438 acid) and Acetobacter (makes to much acetic acid) can intrude and

439 dominate, affecting taste.

440 **

441 Pediococcus is probably less acid tolerant than L. sanfranciscensis, but

442 it grows at higher temperatures (as mentionned above, sanfranciscensis

443 does not like more than 35 - 37°C. Acetobacter is of no importance in

444 sourdoughs: it strictly requires oxygen for growth, and sourdough becomes

445 anaerobic (=without oxygen) very quickly due to the metabolism of yeasts

446 and lactobacilli. If youıve ever seen a vinegar fermenter you will notice

447 that several hundred liter of air are pumped through a liter of vinegar

448 during an hour: it is almost impossible to aerate sourdough in such a way.

449 --------------------------------------------------------------

450 Dr. Sugihara, who participated in the characterization of the flora of San

451 Francisco sourdough and several other cultures, was asked whether natural

452 sourdough cultures could be contaminated with commercial yeast. His reply

453 was no, not if you have a stable culture that is continuously maintained

454 with the same conditions and ingredients.

455 **

456 Dr. Sugihara is certainly right here. There was an experiment done by a

457 Dutch group: bakerıs yeast didnıt survive more than two refreshments. I

458 think that itıs the acetate that kills the yeast as its less acetate

459 tolerant than sourdough yeasts.

460 And to the margin note right next (CONCERNING THE ABILITY OF BACTERIAL

461 FERMENTATION TO RAISE A LOAF OF BREAD, WITHOUT YEAST): Weıve done the

462 experiments, it works quite well without yeast. The volume is somewhat

463 smaller, though. Markus Brandt has estimated the contribution of yeasts

464 and lactobacilli to gas production in a "normal³ sourdough: about 50%

465 comes from lactobacilli and yeasts each. The yeasts are fewer in numbers,

466 but larger in size.

467 --------------------------------------------------------

468 Bakers are interested in the acids produced by leaven microbes because

469 much of the distinctive flavor produced by leaven microbes comes in the

470 form of organic acids that are products of fermentation.

471 **

472 The production of lactic acid in dough in determined mainly by the

473 buffering capacity of the flour, i.e. the ash content. Dough yield and

474 temperature are much less important; as far as Spichers investigations go,

475 I think that the higher lactic acid concent of doughs with higher

476 temperatures or higher dough yields he measured is due mainly to the

477 faster fermentation at these conditions. (this holds true if you calculate

478 the lactate produced on the amount of flour in the dough: this ratio is

479 fairly constant). The amount of acetic acid produced is controlled mainly

480 on the availability of fructose. L. sanfranciscensis produced lactic acid

481 and ethano (and carbon dioxide) from maltose or glucose. If the organism

482 wants to produce the more oxidized end product, acetic acid, another

483 substrate must be reduced. L. sanfranciscensis reduced 2 moles of fructose

484 to mannitol per mole of acetic acid formed. The ratio of mannitol to

485 acetic acid in dough os about 1.8, fairly close to the theoretical value

486 of 2 if fructose was the only co-substrate that is reduced. During

487 fermentation, L. sanfrancisco starts to produce lactic acid and acetic

488 acid first, and forms lactic acid and ethanol only if the fructose is

489 depleted. There is a lot of fructose in dough, but not all of it is

490 available for the lactobacilli. Yeasts liberate some of the fructose bound

491 in glucofructans that thus becomes available for the lactobacilli (there

492 is some nice work that has been done by the Sugihara group, Saunders et

493 al., cereal chemistry, 1972 or 1973). If you to too high with the

494 temperature, you slow down yeast growth, and the acetic acid levels in the

495 dough decrease. For bakers, an easy way to increase the acetic acid

496 content is to add sugar 8that is sucrose,a consisting of glucose and

497 fructose). This wonıt increase the total titrable acidity, though, as that

498 is determined by the buffering capacity. Sugar addition (not too much, 1

499 or 2%) may speed up fermentation in white wheat flours: as mentionned

500 above, in contrast to whole wheat flour and rye flours, the enzyme

501 activities and thus the sugar concentrations are rather low and may limit

502 microbial metabolism.

503 As far as the influence of acetic acid and lactic acid on flavor go:

504 lactic acid has no influence on aroma, only on taste, while acetic acid is

505 an aroma volatile. So, I think it is not so much the ratio of lactic to

506 acetic acid, but more simply the acetic acid content that matters.

507 ------------------------------------------------------------

508 Natural leavens should be actively fermenting and reproducing when they

509 are incorporated into a dough

510 **

511 Yeasts in dough donıt have to rely on oxygen for growth: if that were the

512 case, they woudnı t be there.

513 ----------------------------------------------------------------------

514 The more accepted and consistently successful way to store a culture for a

515 month or so is to make a fresh and very stiff storage leaven, put it in a

516 well covered vessel ...

517 **

518 Such leavens may keep up to almost three month (my sister had a baby in

519 March and didnıt use her starter for almost three month. It was stored the

520 way you described here, and did come out well upon refreshment. The Böcker

521 Reinzuchtsauer is also distributed as stiff, refrigerated product. I think

522 the company does not guarantee storage stability of more than 4 weeks,

523 though.)

524 ----------------------------------------------------------------------

525 Still there may be someone out there who does need to start a leaven

526 because of some terrible misfortune--

527 **

528 I think it does not matter when the first batch of a new sourdough stinks

529 - the good bacilli will come out eventually, and they may come faster if

530 fermentation is done around 25 - 30°C (as mentionned earlier, the

531 temperature optimum of L. sanfranciscensis is 32 - 33°C). There has been

532 nice work done in Rudi Vogels lab on the microflora of a freshly started

533 sourdough: first, there are Enterobacteria (Escherichia coli, Salmonella,

534 Enterobacter), highly undesirable organism that stink terribly, then there

535 are homofermentative lactobacilli (good, but no gas production), then

536 acid-tolerant, heterofermentative lactobacilli. I think, this took about

537 48 hours at 30°C. The stink at the beginning does not matter as the

538 organisms will be diluted out or die eventually. No L. sanfranciscensis,

539 though, these will occur only after repeated refreshments. Peter Stolz of

540 the Böcker company told me that it takes about two weeks of repeated

541 inoculations to get a good "sanfranciscensis³ sourdough. I donıt know

542 whether or not this process was sped up in his case as, due to his

543 workplace, his skin is all covered with L. sanfranciscensis.

544 -----------------------------------------------------------------

545 My biggest disagreement with her, though (NANCY SILVERTON), is about the

546 amount of material one should use in a starter.

547 **

548 I agree with you: one g of dough is one billion lactobacilli and 10

549 million yeasts: more than enough. In the lab, Iım doing most experiments

550 on a 1/10 ml scale, for dough refreshments at home, it does not get much

551 smaller than 10 g: itıs difficult to handle smaller amounts.

552 -------------------------------------------------------------

553 If leaven refreshment intervals are excessive

554 **

555 The main criterion of sourdoughs containing L. sanfranciscensis is the

556 repeated, frequent refreshment (not counted the storage in the

557 refrigerator). Peter Stolz said that one every 24 hours will suffice, if

558 intervals are much longer than that (lets say more than 3 days),

559 different, more acid tolerant organisms may evolve (e.g. L. pontis as

560 found in the Vollmar and Meuser Breasd maschines: these are refreshed

561 frequently, but with a very high inoculum).

562 ---------------------------------------------------------------------

563 Refreshment schedules are always dependent on temperature.

564 **

565 See my earlier comment on the temperature dependency of growth of L.

566 sanfranciscensis and Candida milleri. Most of the typical sourdough yeasts

567 resemble C. milleri with respect to the temperature sensitivity (i.e. no

568 growth at 37°C).

569 -------------------------------------------------------------

570 Acidity can be expressed as flavor (an acid flavor), as pH, or as total

571 acidity.

572 **

573 That a good explanation of the total titrable acidity concept. (I find

574 students almost done with their degree still have difficulties with this

575 concept).

576 -------------------------------------------------------------------

577 At any given temperature the thinner starter will ferment faster and reach

578 a lower pH; but will not contain as much acid.

579 **

580 If you calculate the amount of acid produced on the weight of the flour

581 rather than the dough weight, the outcome -lactic acid per g flour -

582 should be pretty independent on dough consistency (not if very stiff

583 doughs are produced: the combined salt and acid stress leads to a

584 decreased acid production). Markus Brandt observed this in doughs (rye

585 flour, TA 180) if more than 2% salt were added.

586 -------------------------------------------------------------------

587 Together, caramels and Maillard products are responsible for much of the

588 flavor and aroma of fresh yeasted bread, although of these two, Maillard

589 products are moch more intensely aromatic.

590 **

591 This is right for both yeasted breads and sourdough breads, however, it is

592 important to note that whatever chemicals are reacting with each other

593 during baking must be formed during dough fermentation. (Schieberle in

594 Munich has done several nice studies: he supplied doughs with amino acids

595 and demonstrated that the levels of aroma compounds in the bread were

596 increased). So, formation of aroma precursors during dough fermentation is

597 crucial for the Maillard reaction.

598 ==================

599 The end of this set of posts-- DCW

600 --

601 Dan Wing

602 Wagons@connriver.net